GI tract including pancreas is the one of most common primary sites of neuroendocrine tumors. Current grading of neuroendocrine tumors are based on the 2010 WHO classification. This classifies grade 3 tumors as the neuroendocrine tumor with mitosis > 20 per 10 high power field or Ki-67 labeling index > 20%. Etoposide-based chemotherapy, mostly as the combination with cisplatin, has been the mainstay of the treatment for patients with grade 3 neuroendocrine tumors. However, a recent large retrospective analysis has suggested this regimen may not be effective in relatively low Ki-67 labeling index. Therefore, the investigators designed a clinical trial testing temozolomide-capecitabine combination, which has been mostly investigated in well differentiated (ie., grade 1 or 2) neuroendocrine tumors, in patients with grade 3 and low Ki-67 gastroenteropancreatic neuroendocrine tumors.